Method and composition for flaw detection



' Patented Feb. 8, 1949 METHOD AND comrosrrron roa ruiw parse-non Taberdc Forest, Chicago, Ill., as slgnor, by mcsne assignments, to Robert C.Swltzer, South Euclid, Ohio, and Joseph L. Switzcr No firawing,Application May 7, 1945, a Serial No. 592.531

i This invention relates to improvements in methods and compositions fordetecting physical flaws in metallic bodies by the use of fluorescentfinely divided solids employed, particularly, as suspensions in suitableliquids. More specifically. the invention pertains to the elimination ofundesirable secondary fluorescent effects which occasionally or normallylessen the value and sensitivity of such methods.

At the present time, there is knowna magnetic particle method utilizingfluorescent ferromagnetic particles for the purpose of rendering.visible cracks, seams, and porosities in an object treatedtherewithwhen the object is viewed under filtered ultraviolet light in thesubstantial absence of visible light. This method is disclosed in theUnited States Patent No. 2,267,999. The process in question is brieflydescribed as follows.

In proceeding according to this process for inspecting magnetizablemetals, liquid suspensions of ferromagnetic particles are used to locatethe flaws. These particles have a fluorescent substance adhered theretothat is insoluble in the liquid suspending medium. The object, or workpiece, is flrst placed between the poles of a magnetizing unit tomagnetize it, and while magnetized the work piece is immersed in, orflooded with, the liquid suspension of the fluorescent fer- .romagneticparticles. For this purpose, a dilute suspension is used of very finelydivided fluorescent ferromagnetic particles in a suitablesuspendingmedium, preferably a neutral light oil, that will not dissolve thefluorescent substance that a'dheres to the ferromagnetic particles. Theparticles are instantly drawn to the flaws, the opposite sides of whichare generally of opposite magnetic polarity. The particles tend tobridge the gap between the two sides, forming ridges or piles ofparticles at each crack or pore. On rinsing the work piece with lightoil, the ferromagnetic particles of the suspension are largely removedfrom the main surface, while the grouping of the fluorescentferromagnetic particles at the flaws or defects is not disturbed. In theideal case, the background is non-fluorescent. so that when the piece isinspected under filtered near-ultraviolet light, the particles at theflaws give brilliant indications against the non-fluorescent background.

In actual practice it has been found that light 5 oil of the typecommonly used in such a wet mag- 13 Claims." (01.115-183)solidfluorescence of the ferromagnetic particles and the oily backgroundis reduced by liquid fluorescence of the background due to residuallight oil that has not been completely removed.

Further, it is quite usual in actual practice to test parts which have alayer of heavy oil applied to them for rust inhibition purposes. I Also,grease may be introduced into the bath. The heavier oils and grease arehighly fluorescent so that, after-a suspension of fluorescentferromagnetic particles has been in continual use for some time,

the liquid suspending medium may be so highly fluorescent as to providea poorly contrasting background and it may be diflicult to distinguishof the oily suspending medium and of matter disnetic testing method hasa slight fluorescence.

on a part being tested, the contrast between the solved or dispersedtherein may be quenched selectively (to the exclusion of the solidfluorescence of substance intentionally adhered to the suspendedferromagnetic particles) by incorporating with the suspending medium asuitable non-fluorescent dyestuif or other organic material. Thus, thefresh testing liquid will provide a substantially non-fluorescentbackground for the fluorescent ferromagnetic particles, andcontamination of the liquid testing medium with heavy oil, grease orother dissolved or dispersed fluorescent matter will not adverselyaffect the testing by lessening the contrast between the background andthe fluorescent ferromagnetic particles.

It is, therefore, an important object of the present invention toprovide an improved magnetic testing method involving the use of liquidsuspensions of fluorescent ferromagnetic particles which are easilyvisible due to contrast with a substantially non-fluorescent or veryfeebly fluorescent background.

Another important object of the present invention is to provide a methodfor magnetic testing including the step of incorporating with thesuspension of fluorescent. ferromagnetic particles a quenching agentselectively operative on the liquid suspending medium and on fluorescentmat ter dissolved or dispersed therein.

A further object of thepresent invention is to accuses vention willbecome apparent from the following description and appended claims.

proceeding according to my present invention, I dissolve in a liquidsuspending medium for 4 satisfactory. In certain cases, as much as fiveper cent may be necessary.. For the pastes of fluorescent ferromagneticparticles that are diluted to form the testing suspension, a quenchingagent content of six per cent has ordinarily been found satisfactory;These amount of ferromagnetic particles 9. dyestufl or other organicmaterial that will selectively quench the liquid fluorescence of saidsuspending medium as well as the liquid fluorescence of substancesdissolved or dispersed in said suspending medium, for instance, greaseor heavy oil. when light oil or other organic suspending mediaimmiscible with water is employed, I may use, for instance, Sudan YellowGGA, Oil Red 0, Sudan Red III, Oil Soluble Green, Glycolor Green,Glycolor Brown, or other oil soluble dyes that donot fluoresce per seand that have the property of selectively quenching all fluorescence butthat due to solid substances intentionally adhered to the ferromagneticparticles. Besides the specific dyestufls enumerated-I have found thata. number of other dyes very efl'ectively quench the liquid fluorescenceof the suspending medium without quenching the solid fluorescence of theferromagnetic particles. The preferred dyestufi is Sudan Yellow GGA.This dye is quite effective when employed in small amount and hasrelatively little color in normal light in contrast with the red colorin visible light usually characterizing the ferromagnetic particles, ifa red oxide of iron is used in the testing.

Colorless organic materials that form effective quenching agents includealpha naphthyl amine (most efl'ectively employed at 4.25% concentration)and alpha nitro naphthalene (most eflectiveiy employed at 1.75%concentration).

Instead of incorporating the quenching agent directly with the liquidtesting suspension, I may incorporate the quenching agent with therelatively heavy paste frorn'which a testing suspension is often made upby dilution with light oil.

For instance, various ferromagnetic materials in finely divided powderform may have a fluorescent "dyestuff adhered thereto as disclosed inUnited States Patent No. 2,267,999, and then formed into a heav paste asdisclosed in United States Patent No. 2,106,882 by grinding with an oilymedium having dissolved therein a dispersing agent and a dyestui! orother organic material capable of selectively quenching any liquidfluorescence of the testing bath to be made up from the the paste bydilution with a suitable liquid. In making up such pastes, the directionin Patent No. 2,106,882 may be followed with the additional improvementof dissolving my quenching agent disclosed in the present application inany of the vehicles mentioned in the patent.

I may also incorporate the quenching agent, not with the liquid testingsuspension; but with the liquid rinsing medium employed to rinse off thearticle being tested after the same has been subjected to a magneticflux.

The exact amount of dyestufl or other quenching agent employed will varyaccording to the quenching potency of each agent and the amount offluorescence to be quenched. In general, from one-half to two or threeper cent will be found quenching agent will usually compensate for the.fluorescence of the light oil and for that of the fairly large amountof added heavy oil.

As a testing bath gets older it may become slightly fluorescent in spiteof its substantial content of a quenching dyestuif. More quenching agentmay then be added to keep the suspending medium non-fluorescent.

While the mechanism by which the quenching effect is accomplished hasnot been deflnitely established, it is believed that the added quenchingagent may act as a filter for the ultraviolet light, thereby to preventfluorescence. The quenching effect may also be due to the deexcitationof potentially fluorescent molecules. According to this theory, energyis transmitted from an excited potentially fluorescent molecule to thequenching molecule on collision or close contact, with the result thatboth molecules have insufllcient energy for fluorescence. If the energylevels for the two molecules are similar, then resonance may occur whichwould tend to make energy transfer less diiflcult. Thus the quenchingdye will de-excite fluorescent molecules'of oil or substances dlssolvedtherein without tie-exciting the solid fluorescent particles. The reasonwhy some dyes are more effective than others would then be that theycome closer to the energy levels of the oil molecules and of othermolecules dissolved or dispersed in the oil.

Many details of composition and procedure may be varied within a widerange'without departing from the principles of this invention, whichincludes broadly the concept of quenching selectively the fluorescenceof liquid media such as oil and of substances dissolved or dispersedtherein, to provide a vivid contrast between such liquids andfluorescent ferromagnetic particles suspended therein. It is, therefore,not my intention to limit the patent granted on this invention otherwisethan necessitated by the scope of the appended claims.

In these claims, as well as in the specification, I have used the termliquid fluorescence" to designate the fluorescence of the liquidsuspending medium and of matter dissolved or colloidally dispersedtherein, while the term solid fluorescence" has been,used to designatethe fluorescence of solid dyestufls or other solid organic matteradhering to the ferromagnetic particles suspended in the liquid medium.

I claim as my invention: I

l. A composition of matter for detecting flaws in metallic bodiescomprising a liquid suspendingmedium, flnely divided ferromagneticparticles suspended in said liquid, a fluorescent subv stance insolublein said liquid adhered to the in said liquid, a fluorescent substanceinsoluble in said liquid adhered to the surfaces of said ferromagneticparticles, and a non-fluorescent organic dyestufl dissolved in saidliquid capable of selectively quenching any liquid fluorescence in saidorganic suspending medium.

3. A composition of matter for detecting flaws in metallic bodiescomprising a liquid hydrocarbon, finely divided ferromagnetic particlessuspended in said hydrocarbon, a fluorescent substance insoluble in saidliquid adhered to the surfaces of said ferromagnetic particles, and anon-fluorescent organic dyestuff dissolved in said hydrocarbon capableof selectively quenching liquid fluorescence in said hydrocarbon.

4. A composition of matter for detecting flaws in metallic bodiescomprising a liquid hydrocarbon, finely divided ferromagnetic particlessuspended in said hydrocarbon, a fluorescent substance insoluble in saidliquid adhered to the surfaces of said ferromagnetic particles, and thedyestuif Sudan GGA dissolved ,in said hydrocarbon in an amountsufficient for selectively 5. A method for detecting flaws in a metallicarticle comprising creating a magnetic flux in the portion of thearticle comprising the test field, applying to the test field finelydivided ferromagnetic particles in the form of a suspension in a liquidmedium, said particles having a fluorescent substance insoluble in saidliquid adhered thereto, rinsing said test field with a liquid misciblewith said liquid medium, selectively quenching fluorescence of any ofsaid liquids with a non-fluorescent organic dyestufi dissolved in saidrinsing liquid, said rinsing being carried out soas to remove from saidtest field ferromagnetic particles not adhered thereto, and subjectingthe test field to fluorescigenous radiation to render vividly apparentthe location in the test field of ferromagnetic particles adheredthereto. v g

6. A method for detecting flaws in a metallic article comprisingcreating a magnetic flux in the portion of the article comprising thetest' rinsing hydrocarbon, said rinsing being carried out so as toremove from said test field ferro magnetic particles not adheredthereto, and subjecting the test field to fiuorescigenous radiation torender vividly apparent the location in the test fleld of ferromagneticparticles adhered thereto.

7. A method for detecting flaws in a metallic article comprisingcreating a magnetic field in the portion of the article comprising thetest field, applying to the test field finely divided ferromagneticparticles in the form of a suspension in a liquid hydrocarbon, saidparticles having a fluorescent substance insoluble in said liquidadhered thereto, rinsing said test field with a liquid hydrocarbon,selectively quenching fluorescence of said hydrocarbons with thedyestufl Sudan GGA dissolved in said rinsing -hydrocarbon, said rinsingbeing carried out so as to remove from said test field ferromagneticparticles not adhered thereto, and subjecting the test field tofluorescigenous radiation to render vividly apparent the location in thetest fleld of ferromagnetic particles adhered thereto.

8. A-composition of matter comprising a liquid suspending medium,ferromagnetic particles dispersed therein having adhered to the surfacesof said particles a solid fluorescent dyestui'f insoluble in said liquidmedium, and a non-fluorescent organic material dissolved in said liquidmedium capable of selectively quenching any liquid fluorescence in saidmedium.

9. A composition of matter comprising a liquid hydrocarbon,ferromagnetic particles dispersed therein having adhered to the surfacesof said particles a solid fluorescent dyestuif insoluble in saidhydrocarbon, and a non-fluorescent organic dyestuflf dissolved in saidhydrocarbon capable of selectively quenching any liquid fluorescence insaid hydrocarbon.

10. A composition of matter comprising a liquid hydrocarbon,ferromagnetic particles dispersed therein having adhered to the surfacesof said particles a solid fluorescent organic dyestuff insoluble in saidhydrocarbon, and the dyestufl Sudan GGA dissolved in said hydrocarbon inan amount capable of selectively quenching any liquid fluorescence insaid hydrocarbon.

11. A method for detecting flaws in a metallic article comprisingcreating a magnetic flux in the portion of the article comprising thetest field, applying to the test field finely divided ferromagneticparticles in the form of a suspension in a liquid medium, selectivelyquenching fluorescence of said liquid medium with a non-fluorescentcoloring matter dissolved in said medium, said particles having afluorescent substance insoluble in said liquid adhered thereto, rinsingsaid test field with a liquid miscible with said liquid medium andsubjecting the test field to fluorescigenous radiation to render vividlyapparent the location in the test field of ferromagnetic particlesadhered thereto.

12. A composition of matter for detecting flaws in metallic bodiescomprisinga liquid hydrocarbon, finely divided ferromagnetic particlessuspended in said hydrocarbon, a fluorescent substance insoluble in saidliquid adhered to the surface of said ferromagnetic particles, and alphanaphthyl amine dissolved in said hydrocarbon in an amount sufilcient toeffect selective quenching of liquid fluorescence in said hydrocarbon.

13. A composition of matter for detecting flaws in metallic bodiescomprising a liquid hydrocarbon, finely divided ferromagnetic particlessuspended in said hydrocarbon, a fluorescent substance insoluble in saidliquid adhered to the surface of said ferromagnetic particles, and alphanitro naphthalene dissolved in said hydrocarbon in an amount sufilcientto effect selective quetnching of liquid fluorescence in said hydrocaron.

TABER 1)! FOREST.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNI ED STATES manure Number Name Date 1,904,433 Fischer Apr. 18, 19331,988,300 Clark Jan. 15, 1935 2,267,999 Switzer Dec. 30, 1941 2,365,253De Forest "d... Dec. 19, 1944

